Electrochemical polymerisation of phenol in aqueous solution on a Ta/PbO2 anode

This paper deals with the treatment of aqueous phenol solutions using an electrochemical technique. Phenol can be partly eliminated from aqueous solution by electrochemically initiated polymerisation. Galvanostatic electrolyses of phenol solutions at concentration up to 0.1 mol dm−3 were carried out on a Ta/PbO2 anode. The polymers formed are insoluble in acidic medium but soluble in alkaline. These polymers were filtered and then dissolved in aqueous solution of sodium hydroxide (1 mol dm−3). The polymers formed were quantified by total organic carbon (TOC) measurement. It was found that the conversion of phenol into polymers increases as a function of initial concentration, anodic current density, temperature, and solution pH. The percentage of phenol polymerised can reach 15%

Electrochemical Behavior Of N-nitrosothiazolidine Carboxilic Acid On Gold And Mercury Electrodes [comportamento Eletroquímico Da N-nitrosotiazolidina ácido Carboxílico Sobre Eletrodos De Ouro E Mercúrio]

The electrochemical behavior of N-nitrosothiazolidine carboxylic acid (NTAC) on gold and hanging mercury electrodes, using the cyclic and square wave voltammetries, was studied. Whereas NTAC suffer reduction in a single step on the mercury electrode, two peaks appears on the cyclic voltammograms on the gold electrode, one anodic peak overlaying the gold oxide process at 1.2 V and one cathodic peak at -0.41 V vs Ag/AgCl, KCl 3.0 mol L-1. The cathodic peak depends on the previous oxidation of NTAC at the electrode surface, presents irreversible and adsorption controlled characteristics and it is suitable for quantitative purposes.31510671072Douglass, M.L., Kabacoff, B.L., Anderson, G.A., Cheng, M.C., (1978) J. Soc. Cosmet. Chem, 29, p. 581Gray, J.I., Randall, C.J., (1979) J. Food Protection, 42, p. 168(1987) Food Technol, 41, p. 127. , Institute of Food Technologists, Scientific Status Summary;Hotchkiss, J.A., (1987) Addit. Food Res, 31, p. 54Mirvish, S.S., (1975) Toxic. Appl. Pharm, 31, p. 325Walters, C.L., (1992) Food Addit. Contam, 9, p. 441Pensabene, J.W., Fiddler, W., (1994) J. AOAC Int, 77, p. 981Raoul, S., Gremaud, E., Biaudet, H., Turesky, R.J., (1997) J. Agric. Food Chem, 45, p. 4706Andrade, R., Reyes, F.G.R., Rath, S., (2005) Food Chem, 91, p. 173Zhao, Y.Y., Boyd, J., Hrudey, S.E., Li, X., (2006) Environm. Sci. Technol, 40, p. 763Munch, J.W., Bassett, M.V., (2006) J. AOAC Int, 89, p. 496Goicolea, M.A., Balugera, Z.G., Portela, M.J., Barrio, R.J., (1995) Anal. Chim. Acta, 305, p. 310Belal, F., Walash, M.I., Ibrahim, F., Hefnawy, M., Eid, M., (2000) Il Fármaco, 55, p. 694Gorski, W., Cox, J.A., (1994) Anal. Chem, 66, p. 2771Gorski, W., Cox, J.A., (1995) J. Electroanal. Chem, 389, p. 123Cox, J.A., Alberr, K.S., Brockway, C.A., Tess, M.E., Gorski, W., (1995) Anal. Chem, 67, p. 993Collyer, S.D., Bradbury, S., Hatfield, J.V., Higson, S.P.J., (2001) Electroanalysis, 13, p. 332Collyer, S.D., Buther, A.J., Higson, S.P.J., (1997) Electroanalysis, 9, p. 985Bard, A.J., Faulkner, L.R., (2001) Electrochemical Methods: Fundaments and Applications, , John Wiley: New YorkOsteryoung, J.G., O'Dea, J.J.E., (1982) Electroanalytical Chemistry, 14, p. 459. , Bard, A. J, ed, Marcel Dekker: New YorkSouza, D., Machado, S.A.S., Avaca, L.A., (2003) Quim. Nova, 26, p. 81Lovric, M., Komorsky-Lovric, S., (1988) J. Electroanal. Chem, 248, p. 239Long, G.L., Winefordner, J.D., (1983) Anal. Chem, 55, pp. 712ASvensmark, B.O., Organic, E., (1991) Electrochemistry, 3, p. 659. , Marcel Dekker: New Yor

Electroanalytical performance of self-assembled monolayer gold electrode for chloramphenicol determination

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Monolayers of 2-mercapto-5-methylbenzimidazole (MMB) were prepared on a polycrystalline gold electrode via a self-assembly process to produce a self-assembled monolayer. The resulting electrode was investigated by cyclic voltammetry and electrochemical impedance spectroscopy, and applied to the determination of chloramphenicol (CAP) in a pharmaceutical formulation using flow injection analysis along with amperometric detection. The amperometric cell was operated at -0.75 V (vs Ag/AgCl) at a flow rate of 3 mL min(-1). The method was applied to the determination of CAP in ophthalmic solutions, and its performance was compared to a previously validated HPLC method. The response to CAP is linear in the range from 0.050 to 1.000 A mu mol L(-1) (r = 0.9990), and the limit of detection is 44 A mu mol L(-1).16941732345351Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP

Sublethal doses of glyphosate in combination with leaf manganese in marandu grass production

The drift of the herbicide glyphosate can stimulate growth and/or productive yield in non-target plants, which characterizes a hormonal effect, with a momentary yellowing in new leaves, characteristic of nutritional deficiency. Thus, the objective of this work was to evaluate the hormonal effect of glyphosate application in Urochloa brizantha cv. Marandu. The produtive response, aerial (PMS ) and root (MSR), for forage was evaluated by foliar application of seven sublethal doses of equivalent acid (e.a.) to glyphosate (5.40, 10.80, 21.60, 43.20, 64, 80, 86.40 and 108.00 g e.a. ha-1) and control, in the absence and presence of manganese (1000 g ha-1), in the spray solution, in four sequential harvests, featuring a factorial scheme 8 x 2 x 4, with four repetitions. The sublethal doses of glyphosate with the addition of manganese to the spray solution reduced the herbicidal effect, with persistence of PMS during the experimental period (4 cuts). For doses without manganese added to the spray solution, there was a productive failure in the cuts 2, 3 and 4, at doses 86.40 and 108.00 g e.a. ha-1. The presence of manganese in the spray solution ensured a root dry mass superior to those without the addition of manganese, with an effect herbicide in doses equal to and above 43.60 g e.a. ha-1.A deriva do herbicida glifosato pode estimular crescimento e/ou rendimento produtivo em plantas não-alvo, caracterizando efeito hormese. Ainda, manifesta-se amarelecimento momentâneo em folhas novas, característico de deficiência nutricional. Deste modo, o trabalho teve por objetivo avaliar o efeito hormese por aplicação de glifosato em Urochloa brizantha cv. Marandu. Foi avaliada a resposta produtiva aérea (PMS) e radicular (MSR) da forrageira por aplicação foliar de sete doses subletais do equivalente ácido (e.a.) de glifosato (5,40, 10,80, 21,60, 43,20, 64,80, 86,40 e 108,00, g e.a. ha-1) e controle, sob ausência e presença de manganês (1000 g ha-1) à calda de pulverização, em quatro colheitas sequenciais, caracterizando esquema fatorial 8 x 2 x 4, com quatro repetições. As doses subletais de glifosato com adição de manganês à calda de pulverização reduziram o efeito herbicida, com persistência de PMS durante período experimental (4 cortes). Para doses sem adição de manganês à calda de pulverização, houve falência produtiva nos cortes 2, 3 e 4, para doses 86,40 e 108,00 g e.a. ha-1. A presença de manganês à calda de pulverização assegurou massa seca de raiz superior àquelas sem adição de manganês, sendo constatado efeito do herbicida nas doses igual e superiores a 43,60 g e.a. ha-1

Electrochemical behavior of dopamine at a 3,3 '-dithiodipropionic acid self-assembled monolayers

Monolayers of 3,3'-dithiodipropionic acid (DTDPA) were prepared on a polycrystalline gold electrode through a self-assembly procedure to produce a gold 3,3'-dithiodipropionic acid self-assembled monolayer (AuDTDPA) modified electrode. The characterization of the AuDTDPA electrode was investigated by cyclic voltammetry and ac impedance using the [Fe(CN)(6)](3-/4-) redox couple. The electrochemical behavior of DA on the modified electrode AuDTDPA was studied by cyclic and square-wave voltammetries, using phosphate buffer as supporting electrolyte. The oxidation peak current for DA increases linearly with concentration in the range of 0.35 x 10(-5) to 3.4 x 10(-5) mol L-1. The performance of the AuDTDPA modified electrode was evaluated for the electroanalytical determination of dopamine (DA) in a pharmaceutical formulation. The AuDTDPA modified electrode showed a stable behavior and the presence of surface-COOH groups avoided the passivation of the electrode surface during the dopamine oxidation. (c) 2006 Elsevier B.V. All rights reserved.72242743

Electrochemical behavior of nicotine studied by voltammetric techniques at boron-doped diamond electrodes

The electrochemical behavior of nicotine in alkaline media was studied using a boron doped diamond (BDD) surface as the working electrode. In order to establish the pH dependence and to gain information about the mass transport of the species, cyclic voltammetry studies were carried out in a 0.1 mol L-1 BR (Britton-Robinson) buffer in the presence of 1.0 x 10(-3) mol L-1 nicotine. The optimum pH value was 8 and the mass transport was controlled by diffusion of the species. The square wave voltammetry technique was used to determine the electroanalytical parameters such as frequency, amplitude, and scan increment. After optimization, an analytical curve was constructed. The limits of detection and quantification were 0.50 and 1.66 mg L-1, respectively. Theoretical calculations indicate that the probable oxidation site on the nicotine molecule was the nitrogen atom denoted "11N" and a speculation about the reaction mechanism was proposed. Finally, an experiment using a real sample (cigarette tobacco) was carried out and a recovery study revealed a value of about 4.3 mg L-1 in 0.1 g of tobacco.38101587159

Nutritional value of forage peanut (Arachis Pintoi cv. BRS Mandobi) and elephant grass silages.

Arachis pintoi, commonly known as forage peanut, is a leguminous plant with good forage yield and nutritional quality adapted to the Brazilian environmental conditions and used in grass/legume pastures or preserved as silage or hay. In this study, we evaluated the nutritional value and dry matter losses of silages produced with different proportions of forage peanutcv. BRS Mandobi and elephant grass. Five levels of substitution of elephant grass (0, 25, 50, 75, and 100%, fresh matter basis) for the legume were tested in a completely randomized design with four replicates. The fiber components of the silages, except lignin, decreased with higher levels of forage peanut. Crude protein content and in vitro dry matter digestibility presented maximum values of 16.9% and 62.5%, increasing by 0.07 and 0.15 units with every 1% of the legume added to the silage, respectively. Silage pH rose from 3.8 to 5.4, although gas and effluent losses had estimated reductions of 0.01 and 0.66 units for each additional unit of the legume. Silages composed of elephant grass and more than 50% forage peanut improve the nutritional value of the feed and increase dry matter recovery of the ensiled forage mass. Silages with these proportions of forage peanut have high protein and low fiber contents.bitstream/item/196785/1/26794.pd